The present invention relates to a composite material for electromagnetic shielding.
The function of electromagnetic shielding is to eliminate or a least reduce the amount of energy radiated into a certain space or the electromagnetic radiation emitted from a space. Shields of the type in question are variously required for avoiding extraneous diffusion into cables and electronic circuits, for suppressing illegal broadcasts from monochromatic or even wide-band jamming stations or even for personnel protection, more particularly as radiation protection in the microwave range. The shielding effect is based on two factors: firstly, some of the incident radiation is reflected at the surface of the shield and, secondly, that part of the radiation which penetrates into the medium is continuously absorbed as it passes through the shield. A shielding material is required on the one hand to combine high conductivity with minimal thickness (metal shield) so that the degree of reflection is high. Problems can arise at seams. In the event of unsatisfactory, seamless contacting over a large surface, stray fields are capable of entering the shielded space. On the other hand, the shield may be constructed as a "black body" which absorbs all the radiation and converts it into heat. It is possible in this way to avoid surface currents and to eliminate contacting problems. However, there is no such thin as a universally usable shielding material because the wave impedance of the long-range field does not have the same values as in the short-range field, although on the other hand it is essential in a black body for the wave impedance of the space to be adapted to the surface resistance of the body.